1 files changed, 1 insertions, 1 deletions
diff --git a/Source/Core/Duplicator.cs b/Source/Core/Duplicator.cs
index 4350571a..becd1791 100644
--- a/Source/Core/Duplicator.cs
+++ b/Source/Core/Duplicator.cs
@@ -214,7 +214,7 @@ namespace Microsoft.Boogie {
       Contract.Ensures(Contract.Result<Expr>() != null);
       return base.VisitExpr((Expr)node.Clone());
     }
-    public override List<Expr> VisitExprSeq(List<Expr> list) {
+    public override IList<Expr> VisitExprSeq(IList<Expr> list) {
       //Contract.Requires(list != null);
       Contract.Ensures(Contract.Result<List<Expr>>() != null);
       return base.VisitExprSeq(new List<Expr>(list));